feat: add SandBase Harness MCP server

[liyangbing]

Summary\n- add the official SandBase Harness MCP bridge as a structured registry entry\n- document its six stdio tools, Docker image, runtime URL, and optional API key\n- qualify that execution isolation depends on the selected backend and deployment configuration\n\n## Verification\n- OpenModels MCP Server Registry Validator

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Validating MCP server registry...

✅ Validation Passed

Validated 209 files successfully.\n- \n\nThe entry is source-backed by the SandBase Harness repository and installation guide. It does not claim a hosted endpoint, universal isolation, endorsement, or security certification.

[liyangbing]

Verification from the submitted revision:

• python3 validate.py passed: 209 files validated successfully.
• git diff --check passed.
• The entry points to the official repository and the pinned ghcr.io/sandbaseai/sandbase-harness-mcp:0.3.8 image.
• MANAGED_AGENTS_URL is required; MANAGED_AGENTS_API_KEY is optional when runtime authentication is enabled.
• The description explicitly states that execution isolation depends on the selected backend and deployment configuration; no hosted endpoint, universal isolation, endorsement, or security certification is claimed.

Maintainer review remains authoritative.

[madeburo]

hi @liyangbing
The entry validates successfully, the pinned 0.3.8 image is available for both amd64 and arm64, and the six tool definitions match the v0.3.8 source.

There is one install configuration discrepancy to address. The canonical SandBase MCP configuration includes:

--add-host=host.docker.internal:host-gateway

The submitted Docker arguments omit it. Without this mapping, the MCP container may be unable to reach a Harness runtime running on the same Linux host. Please add the argument so the registry configuration matches the official installation.

PR #20 adds the same sandbase-harness entry but contains outdated tool schemas. Once this change is made, I suggest keeping this PR and closing #20 as superseded.